Pneumatic tire

ABSTRACT

To provide a pneumatic tire excellent in steering stability and durability at high-speed driving, it is provided a pneumatic tire having a tread portion and a belt layer, wherein the tread portion is arranged on the outer side of the belt layer in the tire radial direction, the reinforcing cord in the belt layer is composed of cords made of monofilaments in which 50/5 cm or more of the monofilaments are arranged in the tire width direction in the tire radial cross section of the belt layer, and the maximum load capacity of the tire WL (kg) and the weight of the tire WT (kg) satisfy (WT/WL)≤0.0140.

TECHNICAL FIELD

The present invention relates to pneumatic tires, more particularly pneumatic tires with a belt layer.

BACKGROUND ART

In recent years, from the viewpoint of increasing interest in environmental issues and economic efficiency, there has been an increasing demand for fuel efficiency in automobiles and for improved fuel efficiency of pneumatic tires (hereinafter, simply referred to as “tires”) installed in automobiles as well.

The fuel efficiency of a tire can be evaluated by the rolling resistance, and it is known that the smaller the rolling resistance, the better the fuel efficiency of the tire.

Therefore, conventionally, it has been proposed to reduce the rolling resistance by devising the composition of the rubber composition constituting the tread portion of the tire (for example, Patent Documents 1 to 4).

In addition to the above, the development of technology for reducing the weight of tires, for example, technology for reducing the weight of carcass, belts, beads, etc., has become active.

PRIOR ART DOCUMENT Patent Document

-   Patent Document 1: JP-A-2018-178034 -   Patent Document 2: JP-A-2019-089911 -   Patent Document 3: WO2018/186367A1 -   Patent Document 4: JP-A-2019-206643

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, nowadays, high-speed driving has become common due to the well-developed highways, and it was found that there is a concern about ensuring steering stability and durability during high-speed driving when the maximum load capacity of tires WL (kg) and the weight of tires WT (kg) satisfy the following formula 1.

(WT/WL)≤0.0140  formula 1

Therefore, an object of the present invention is to provide pneumatic tires with excellent steering stability and durability at high speeds even when the tires are lighter than a certain level.

Means for Solving Problems

The present inventor has earnestly studied the solution to the above problem, found that the above problem can be solved by the invention described below, and completed the present invention.

The invention according to claim 1 is:

a pneumatic tire having a tread portion and a belt layer, wherein the tread portion is arranged on the outer side of the belt layer in the tire radial direction,

the reinforcing cord in the belt layer is composed of cords made of monofilaments in which 50/5 cm or more of the monofilaments are arranged in the tire width direction in the tire radial cross section of the belt layer, and the maximum load capacity of the tire WL (kg) and the weight of the tire WT (kg) satisfy the following formula 1.

(WT/WL)≤0.0140  formula 1

The invention according to claim 2 is:

the pneumatic tire according to claim 1, wherein the outer diameter of the cord made of the monofilaments is 0.1 to 0.5 mm.

The invention according to claim 3 is:

the pneumatic tire according to claim 1 or 2, wherein the complex elastic modulus E* (MPa) when the tread rubber composition forming the contact surface in the outermost layer of the tread portion is measured under the conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, deformation mode: elongation, and the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer satisfy the following formula 2.

(E*×T)≥30  formula 2

The invention according to claim 4 is:

the pneumatic tire according to any one of claims 1 to 3, wherein the tread portion has a plurality of circumferential grooves extending continuously in the tire circumferential direction, and the total cross-sectional area of the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of the tread portion.

The invention according to claim 5 is:

the pneumatic tire according to any one of claims 1 to 4, wherein the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion.

The invention according to claim 6 is:

the pneumatic tire according to any one of claims 1 to 5, wherein at least two layers of the belt layer are provided, and the average distance D (mm) between the belt layers in the tread portion is 0.6 mm or less, in at least one set of belt layers adjacent to each other in the radial direction of the tire.

The invention according to claim 7 is:

the pneumatic tire according to any one of claims 1 to 6, wherein at least two layers of the belt layer are provided, and the angle between the belt layers in the tread portions in the tire circumferential direction is 65° or less, in at least one set of belt layers adjacent to each other in the radial direction of the tire.

The invention according to claim 8 is:

the pneumatic tire according to any one of claims 1 to 7, wherein the tread has a circumferential groove extending continuously in the tire circumferential direction, and the ratio (L₈₀/L₀) of the groove width L₈₀ at a depth of 80% of the maximum depth of the circumferential groove to the groove width L₀ of the circumferential groove on the contact surface of the tread portion is 0.3 to 0.7.

The invention described in 9 is:

the pneumatic tire according to any one of claims 1 to 8, wherein the tire cross-sectional width Wt (mm) is less than 200 mm.

Effect of the Invention

According to the present invention, it is possible to provide a pneumatic tire having excellent steering stability and durability at high-speed driving even if the weight of the tire is reduced to a certain level or more.

EMBODIMENTS FOR CARRYING OUT THE INVENTION [1] Characteristics of the tire according to the present invention

First, the characteristics of the pneumatic tire according to the present invention will be described.

1. Overview

The tire according to the present invention is a tire provided with a belt layer and a tread portion, and the maximum load capacity WL (kg) of the tire and the weight WT (kg) of the tire have the following relationship (following 1).

(WT/WL)≤0.0140  formula 1

The tread portion is arranged outside in the tire radial direction of the belt layer, and the reinforcing cord in the belt layer is a cord made of monofilament (hereinafter, also referred to as “monofilament cord”) arranged 50 lines/5 cm or more in the tire width direction in the tire radial cross section of the belt layer.

By configuring as described above, even if the weight of the tire is reduced to a certain level or more, specifically, the maximum load capacity WL (kg) of the tire and the weight WT (kg) of the tire satisfy the relation of the above (formula 1), it is possible to provide a pneumatic tire having excellent steering stability and durability during high-speed driving.

In the above description, the “maximum load capacity WL” refers to a value calculated using the following two formulas based on tire cross-sectional width Wt (mm), the tire cross-sectional height Ht (mm), and the tire outer diameter Dt (mm) in a state where the tire is assembled to a regular rim, has an internal pressure of 250 kPa and is in no load state; and is about 50 to 100 kg smaller than the maximum load capacity based on the road index (LI) defined by the JATTA standard (Japan Automobile Tire Association standard). Note that V is the volume of the space occupied by the tire (virtual volume), and (Dt/2−Ht) is the rim diameter.

V (mm³)={(Dt/2)²−(Dt/2−Ht)² }×π×Wt

WL (kg)=0.000011×V+100

Here, the “regular rim” is a rim defined for each tire in the standard system including the standard on which the tire is based. For example, in the case of JATTA (Japan Automobile Tire Association), standard rims in applicable sizes described in “JATTA YEAR BOOK”, in the case of ETRTO (The European Tire and Rim Technical Organization), “Measuring Rim” described in “STANDARDS MANUAL”, and in the case of TRA (The Tire and Rim Association, Inc.), “Design Rim” described in “YEAR BOOK” mean the “regular rim”. In the case of tires that are not specified in the standard, it means a rim having the smallest rim diameter, and then having the narrowest width among the rims which can be assembled and the internal pressure can be maintained, that is, rims not causing air leakage between the rim and the tire.

The tire cross-sectional width Wt can be obtained as a width obtained by excluding the pattern and characters on the side surface of the tire from the direct distance (total width of the tire) between the sidewalls including all the patterns and characters on the side surface of the tire. Further, the tire cross-sectional height Ht can be obtained as ½ of the difference between the outer diameter of the tire and the nominal diameter of the rim.

2. Mechanism of Effect Manifestation in Tire According to the Present Invention

The mechanism for exhibiting the effect of the tire according to the present invention, that is, the mechanism for achieving both steering stability and durability at high-speed driving even if the weight of the tire is reduced to a certain level or more, is presumed as follows.

As one of the methods for improving the fuel efficiency of a tire, it is conceivable to reduce the weight of the tire by reducing the amount of the tire members (thickness) constituting the tire. However, when the amount of the tire member is reduced, the rigidity of the tire is lowered and the moment of inertia is also reduced, which may lead to a decrease in steering stability.

Especially, when driving at high speeds, the tread is likely to be rounded due to centrifugal force. Therefore, it is considered that the steering stability is significantly reduced, and at the same time, the amount of deformation of the tire during rolling is increased and the durability is also significantly reduced.

Specifically, when the maximum load capacity of the tire WL (kg) and the weight of the tire WT (kg) have the relationship of the following (formula 1), there is concern about ensuring steering stability and durability during high-speed driving.

(WT/WL)≤0.0140  (formula 1)

Therefore, in the present invention, the belt layer for reinforcing the tread is configured by using a cord made of monofilament (single wire) (monofilament cord) instead of a cord made of twisted wire (twisted cord). By adopting a monofilament cord as a reinforcing cord, unlike a twisted cord, elongation is unlikely to occur, so that elongation of the belt layer can be suppressed. Further, by arranging 50 or more monofilament cords per 5 cm, that is, by arranging the cord in a dense state at intervals of 1 mm or less per one line, the belt layer can exert sufficient restraint on the tread part, and as a result, even when driving at high speed with lightweight tires, it is considered that the tread portion is unlikely to be rounded, and steering stability and durability at high-speed driving can be ensured.

Then, it was found that, by adopting the above configuration, even if (WT/WL)≤0.0140 (formula 1), steering stability and durability can be obtained at a sufficiently high-speed driving. Even if (WT/WL) is set to 0.0135 or less to sufficiently reduce the rolling resistance and achieve low fuel consumption, steering stability and durability at high-speed driving are sufficiently attained. It was found that a further effect can be obtained by setting (WT/WL) to 0.0133 or less to further reduce the weight.

The arranged number of monofilaments refers to the average number of cords arranged in the tire width direction per 5 cm in a state where the tire is assembled to a regular rim, has an internal pressure of 250 kPa and is in no load state. Simply it can be obtained by measuring the number of cords arranged in a width of 5 to 10 cm around the equatorial plane of the tire on the section cut out in the tire radial direction with a thickness of 2 to 4 cm and calculating the average number of cords per 5 cm.

The cord outer diameter of the monofilament cord described above is preferably 0.1 mm or more and 0.5 mm or less. If it is less than 0.1 mm, the force that can be generated by one monofilament is weak, and there is a possibility that sufficient restraint force cannot be exerted. At the same time, it is considered that it is likely to break due to an impact during driving, and there is a concern that the effect of improving high-speed steering stability and durability performance will decrease.

On the other hand, if the outer diameter of the cord is more than 0.5 mm, when the monofilament cords are arranged, it may be difficult to cover the monofilament cords with rubber without gaps to form a belt layer. At the same time, since the distance between the monofilament cords becomes narrow, the monofilament cord layer is less likely to be deformed in the width direction during turning, and it is not possible to generate sufficient stress, and there is a concern that the effect of improving steering stability will be reduced.

For the above reason, the outer diameter of the cord is more preferably 0.15 mm or more, and further preferably 0.2 mm or more. On the other hand, the upper limit is more preferably 0.40 mm or less, and further preferably 0.35 mm or less. The cord outer diameter of the monofilament cord described above refers to the outer diameter of the monofilament cord in the tire width direction in the tire, and when the cord cross section is a perfect circle, it is equal to the normal outer diameter. When the cord has a flatness, the outer diameter is defined by the distance occupied in the tire width direction obtained by Φ×cos θ, where the major axis of the cord is Φ (mm) and the angle formed by the major axis Φ and the line parallel to the tire width direction is θ.

[2] A More Preferable Aspect of the Tire According to the Present Invention

The tire according to the present invention can obtain a larger effect by taking the following aspects.

1. Complex Elastic Modulus of Tread Rubber and Distance from Tread to Belt Layer

In the tire according to the present invention, it is preferable that the complex elastic modulus E* (MPa) when the tread rubber composition forming the contact surface in the outermost layer of the tread portion is measured under the conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, deformation mode: elongation and the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer satisfy (E*×T)≥30 (formula 2).

The complex elastic modulus E* is a parameter related to rigidity, and the larger the value, the higher the rigidity, and the occurrence of rounding of the tread portion during high-speed driving can be suppressed. It is considered that, at the same time, a large reaction force to the tread surface is easier to obtain. Further, since the rigidity of the entire tread surface can be increased, it is considered that it becomes easier to suppress the large deformation of the tread portion when an impact is transmitted.

On the other hand, the distance from the outermost surface of the tread portion to the outermost surface of the belt layer can be considered as a parameter indicating the effect of tightening the belt layer due to the rigidity of the tread portion, it is considered that the larger the value, the restraint by belt layer can be sufficiently secured. At the same time, since the larger the value, the more the distance from the tread surface to the belt layer is maintained, it is considered that the deformation of the belt layer in the tire radial direction can be reduced.

Based on this idea, experiments were conducted on the preferable relationship between the complex elastic modulus E* (MPa) and the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer, and as a result, it was found that the restraint by belt layer can be sufficiently secured, and at the same time, the amount of deformation of the belt layer in the tire radial direction can be reduced and steering stability and durability at high-speed driving can be improved, if the above-mentioned relationship of (E*×T)≥30 is satisfied.

In the above description, the complex elastic modulus E* can be measured using, for example, a viscoelasticity measuring device such as “Iplexer (registered trademark)” manufactured by GABO. (E*×T) is more preferably 35 or more, and further preferably 40 or more.

In the above description, the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer is the direct distance from the tread surface on the tire equatorial plane to the monofilament cord surface of the outermost layer of the belt layer in the tire radial cross section when the tire is assembled on a regular rim, has an internal pressure of 250 kPa and is in no load state.

When a groove is formed on the equatorial surface of the tread, the distance T is defined as the distance from the intersection of the line obtained by connecting the ends of the groove at tire contact surface and the equatorial surface of the tire to the outermost layer of the belt layer. When the monofilament cord of the outermost layer of the belt layer does not exist on the equatorial plane of the tire, the distance T is obtained by using the intersection of the line connecting the two points on the outermost side in the tire radial direction of the pair of monofilament cords closest to the equatorial plane and the equatorial plane as the position of the outermost layer of the belt layer.

The distance T (mm) can be simply measured in a state where the bead portion of the section cut out in the tire width direction with a thickness of 2-4 cm is pressed down according to the corresponding rim width.

The upper limit of the complex elastic modulus E* of the rubber composition is not particularly limited, but it is preferably 15.0 MPa or less, more preferably 12.0 MPa or less, and further preferably 9.0 MPa or less.

If it exceeds 15.0 MPa, it is considered that the tread portion is less likely to be deformed, and it becomes difficult to obtain the effect of improving the steering stability during high-speed driving. On the other hand, the lower limit is not particularly limited, but is preferably 3.0 MPa or more, more preferably 3.7 MPa or more, and further preferably 5.0 MPa or more. If it is less than 3.0 MPa, the rigidity of the tread portion becomes low and the amount of deformation becomes too large, so that it is considered difficult to obtain the effect of improving the durability performance.

The distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer is preferably 12.0 mm or less, more preferably 10.0 mm or less, and further preferably 7.5 mm or less.

If it exceeds 12.0 mm, the distance from the surface of the tread portion to the belt layer becomes too long, it becomes difficult to transmit the shear deformation generated on the surface of the tread portion to the belt layer, and it becomes difficult to obtain a sufficient reaction force. It is considered that it will be difficult to obtain the effect of improving the steering stability at the high-speed driving. The lower limit is preferably 6.0 mm or more, more preferably 7.0 mm or more. If it is less than 6.0 mm, the impact from the tread portion is easily transmitted to the belt layer, so that it is considered difficult to obtain the effect of improving durability performance.

2. Groove on the Tread

In the tire according to the present invention, the tread portion has a plurality of circumferential grooves, and it is preferable the total cross-sectional area of the plurality of circumferential grooves is 10% or more and 30% or less of the cross-sectional area of the tread portion. As a result, the movement of the tread portion can be suppressed, and the steering stability and durability at high-speed driving can be sufficiently improved. It is more preferably 15% or more and 27% or less, further preferably 18% or more and 25% or less, and particularly preferably 21% or more and 23% or less.

The cross-sectional area of the tread portion described above refers to the area outside the tire radial direction from the belt layer in the region separated by a straight line connecting the circumferential groove ends of the tread portion and two straight lines parallel to the equatorial plane that pass through both ends of the widest among the tread surface profile formed by the tread surface and belt layer, in the radial cross section of the tire mounted on a regular rim, having an internal pressure of 250 kPa and in no-load state.

When a belt reinforcing layer using organic fibers and/or steel cords is provided on the outer side in the radial direction of the tire from the belt layer, it refers to the area on the outer side in the radial direction of the belt reinforcing layer. The cross-sectional area of the circumferential groove refers to the total value of the area composed of a straight line connecting the ends of the tread circumferential groove and a groove wall in a tire mounted on a regular rim, having an internal pressure of 250 kPa and is in no-load state. Simply, it is possible to obtain in a state where the bead portion of the section cut out in the tire radial direction with a width of 2 to 4 cm is pressed down according to the rim width.

Further, it is preferable that the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is 2.0% or more and 5.0% or less of the volume of the tread portion. As a result, the movement of the tread portion can be suppressed, and the steering stability and durability at high-speed driving can be sufficiently improved. It is more preferably 2.2% or more and 4.0% or less, further preferably 2.5% or more and 3.5% or less, and particularly preferably 2.7% or more and 3.0% or less.

The volume of the tread portion described above refers to the volume obtained by extending the area of the tread portion in the tire circumferential direction. Simply, it can be obtained by multiplying the area of the tread portion and the length of the outer circumference of the tire (outer diameter Dt×π). The volume of the lateral groove refers to the total of the volume composed of the surface connecting the ends of the lateral groove and the groove wall in a tire mounted on a regular rim, having an internal pressure of 250 kPa and in a no-load state. It can be calculated by obtaining the volume of each lateral groove.

Further, the ratio of the groove width L₈₀ (L₈₀/L₀) at a depth of 80% of the maximum depth of the circumferential groove to the groove width L₀ of the circumferential groove on the contact surface of the tread portion is preferably 0.3 or more and 0.7 or less. As a result, the movement of the entire land portion can be suppressed on the bottom surface of the land portion of the tread portion, and the steering stability and durability at high-speed driving can be sufficiently improved. It is more preferably 0.35 or more and 0.65 or less, further preferably 0.40 or more and 0.60 or less, and particularly preferably 0.45 or more and 0.55 or less.

The above-mentioned L₀ and L₈₀ refer to the direct distance (L₀) between the groove end portions of the tread circumferential groove on the tread surface portion of the tire and the minimum distance (L₈₀) between the groove wall at a groove depth of 80% in a tire mounted on a regular rim, having internal pressure of 250 kPa and in a no-load state. Simply, it is possible to obtain in a state where the bead portion of the section cut out in the tire radial direction with a width of 2 to 4 cm is pressed down according to the corresponding rim width.

3. Multi-Layered Belt Layer

In the present invention, at least two belt layers are provided to form a multi-layer structure, and in at least one set of belt layers adjacent to each other in the radial direction of the tire, the average distance D (mm) between the belt layers in the tread portion is preferably 0.6 mm or less.

As a result, one set of belt layers can cooperate with each other to appropriately restrain the tread portion and suppress the amount of deformation of the tread portion at the time of rolling, and the steering stability and durability at high-speed driving can be further improved.

The average distance D between the belt layers referred to here is the average distance between the monofilaments (cords) of the belt layers, and is equal to the distance between the outer surface of the monofilament of the inner belt layer and the inner surface of the monofilaments of the belt layer on the surface side of the two overlapping belt layers on the equatorial plane.

Further, in the case of a multi-layered belt layer, in at least one set of belt layers adjacent to each other in the radial direction of the tire, the angle formed by the belt layers in the tire circumferential direction at the tread portion is preferably 65° or less. more preferably 60° or less, and further preferably 58° or less.

By arranging the belt layers that are inclined to each other at an appropriate angle, it is possible to obtain a tightening effect, firmly restrain almost the entire width of the tread portion, and suppress the amount of deformation of the tread portion during rolling. Thus, low rolling resistance and steering stability can be maintained.

The angle is the angle of the monofilament with respect to the tire circumferential direction when the tire is not filled with air, and can be confirmed by peeling the tread portion from the outside in the radial direction of the tire.

Further, by arranging the belt layers that are inclined to each other at an appropriate angle, it is possible to firmly restrain almost the entire width of the tread portion and suppress the amount of deformation of the tread portion during rolling, so that steering stability during high-speed driving and the durability can be further improved.

4. Tire Shape

In the tire according to the present invention, when the tire is assembled to a regular rim and has the internal pressure of 250 kPa, the specific tire outer diameter Dt (mm) is, for example, preferably 515 mm or more, more preferably 558 mm or more, further more preferably 585 mm or more, particularly preferably 658 mm or more, and most preferably 673 mm or more. On the other hand, it is preferably less than 843 mm, more preferably less than 725 mm, and further more preferably less than 707 mm.

The specific tire cross-sectional width Wt (mm) is, for example, preferably 115 mm or more, more preferably 130 mm or more, further preferably 150 mm or more, still more preferably 170 mm or more, particularly preferably 185 mm or more, and most preferably 193 mm or more. On the other hand, it is preferably less than 305 mm, more preferably less than 245 mm, further preferably less than 210 mm, particularly preferably less than 205 mm, and most preferably less than 200 mm.

The specific tire cross-sectional height Ht (mm) is, for example, preferably 37 mm or more, more preferably 87 mm or more, and further preferably 95 mm or more. On the other hand, it is preferably less than 180 mm, more preferably less than 112 mm, and further more preferably less than 101 mm.

And, the specific value of the above-mentioned V (virtual volume) is, for example, preferably 13,000,000 mm³ or more, more preferably 29,000,000 mm³ or more, and further preferably 36,000,000 mm³ or more. On the other hand, it is preferably less than 66,000,000 mm³, more preferably less than 44,000,000 mm³, and further preferably less than 38,800,000 mm³.

Further, in the present invention, considering the stability during driving, (Dt−2×Ht) is preferably 450 (mm) or more, more preferably 470 (mm) or more, and further preferably 480 (mm). On the other hand, considering the deformation of the tread portion, it is preferably less than 560 (mm), more preferably less than 530 (mm), and further more preferably less than 510 (mm).

[3] Embodiment

Hereinafter, the present invention will be specifically described based on the embodiments.

1. Rubber Composition Constituting the Outermost Layer of the Tread Portion (1) Compounding Material

The rubber composition forming the outermost surface layer of the tread portion of the tire according to the present invention (tread rubber composition) for can be obtained from the rubber components described below and other compounding materials.

(a) Rubber Component

In the present embodiment, the rubber component is not particularly limited, and rubber (polymer) generally used in the manufacture of tires can be used. Examples thereof include diene rubber such as isoprene-based rubber, butadiene rubber (BR), styrene butadiene rubber (SBR), and nitrile rubber (NBR), and butyl rubber such as butyl rubber. These may be used alone or in combination of two or more, but it is preferable to contain any one of isoprene-based rubber, BR, and SBR and isoprene-based rubber. It may contain isoprene-based rubber and BR, BR and SBR, isoprene-based rubber and SBR, or isoprene-based rubber and BR and SBR.

(A) SBR

For example, the content of SBR in 100 parts by mass of the rubber component is preferably more than 50 parts by mass, more preferably more than 75 parts by mass, further preferably more than 80 parts by mass, and particularly preferably more than 85 parts by mass, for example, from the viewpoint of steering stability during high-speed driving. On the other hand, it is preferably less than 100 parts by mass, and more preferably less than 95 parts by mass, from the viewpoint of heat generation during high-speed driving.

For example, the weight average molecular weight of SBR is more than 100,000 and less than 2 million. The styrene content of SBR is preferably more than 5% by mass, more preferably more than 10% by mass, and further more preferably more than 20% by mass, for example, from the viewpoint of obtaining steering stability at high-speed driving. On the other hand, from the viewpoint of heat generation and durability performance during high-speed driving, it is preferably less than 50% by mass, more preferably less than 40% by mass, and further more preferably less than 35% by mass. For example, the vinyl bond amount (1,2-bonded butadiene unit amount) of SBR is more than 5% by mass and less than 70% by mass. The structure identification of SBR (measurement of styrene content and vinyl bond amount) can be performed using, for example, an apparatus of the JNM-ECA series manufactured by JEOL Ltd.

The SBR is not particularly limited, and for example, emulsion-polymerized styrene-butadiene rubber (E-SBR), solution-polymerized styrene-butadiene rubber (S-SBR) and the like can be used. The SBR may be either a non-modified SBR or a modified SBR.

The modified SBR may be any SBR having a functional group that interacts with a filler such as silica. Examples thereof include SBR (terminal modified SBR having the functional group at the end) in which at least one end of the SBR is modified with a compound having the above functional group (modifying agent), main chain modified SBR having the functional group in the main chain, and main chain terminal modified SBR having the functional group in the main chain and the terminal (for example, main chain terminal modified SBR having the above functional group in the main chain and at least one end modified with the above modifying agent) and terminally modified SBR which is modified (coupling) by a polyfunctional compound having two or more epoxy groups in the molecule and into which a hydroxyl group or an epoxy group has been introduced.

Examples of the functional group include an amino group, an amide group, a silyl group, an alkoxysilyl group, an isocyanate group, an imino group, an imidazole group, a urea group, an ether group, a carbonyl group, an oxycarbonyl group, a mercapto group, a sulfide group, a disulfide group, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, an ammonium group, an imide group, a hydrazo group, an azo group, a diazo group, a carboxyl group, a nitrile group, a pyridyl group, an alkoxy group, a hydroxyl group, an oxy group and an epoxy group. These functional groups may have a substituent.

Further, as the modified SBR, for example, an SBR modified with a compound (modifying agent) represented by the following formula can be used.

In the formula, R¹, R² and R³, which are the same or different, represent an alkyl group, an alkoxy group, a silyloxy group, an acetal group, a carboxyl group (—COOH), a mercapto group (—SH) or a derivative thereof; R⁴ and R⁵, which are the same or different, represent hydrogen atom or an alkyl group, and R⁴ and R⁵ may combine to form a ring structure with nitrogen atoms; and n represents an integer.

As the modified SBR modified by the compound (modifier) represented by the above formula, SBR in which the polymerization end (active end) of the solution-polymerized styrene-butadiene rubber (S-SBR) is modified by the compound represented by the above formula (modified SBR described in JP-A-2010-111753 or the like) can be used.

Alkoxy groups are preferable as R¹, R² and R³ (preferably an alkoxy group having 1 to 8 carbon atoms, and more preferably an alkoxy group having 1 to 4 carbon atoms). Alkyl groups (preferably alkyl groups having 1 to 3 carbon atoms) are suitable as R⁴ and R⁵. Preferably, n is 1 to 5, more preferably 2 to 4, and further more preferably 3. Further, when R⁴ and R⁵ are combined to form a ring structure together with a nitrogen atom, a 4 to 8-membered ring is preferable. The alkoxy group also includes a cycloalkoxy group (cyclohexyloxy group, etc.) and an aryloxy group (phenoxy group, benzyloxy group, etc.).

Specific examples of the above modifiers include 2-dimethylaminoethyltrimethoxysilane, 3-dimethylaminopropyltrimethoxy-silane, 2-dimethylaminoethyltriethoxysilane, 3-dimethylaminopropyl-triethoxysilane, 2-diethylaminoethyltrimethoxysilane, 3-diethylaminopropyl-trimethoxysilane, 2-diethylaminoethyltriethoxysilane, and 3-diethyl-aminopropyltriethoxysilane. These may be used alone or in combination of two or more.

Further, as the modified SBR, a modified SBR modified with the following compound (modifier) can also be used. Examples of the modifier include polyglycidyl ethers of polyhydric alcohols such as ethyleneglycol diglycidyl ether, glycerin triglycidyl ether, trimethylolethane-triglycidyl ether and trimethylolpropane triglycidyl ether;

polyglycidyl ether of aromatic compound having two or more of phenol group such as diglycidylated bisphenol A; polyepoxy compounds such as 1,4-diglycidylbenzene, 1,3,5-triglycidylbenzene, and polyepoxidized liquid polybutadiene; epoxy group-containing tertiary amines such as 4,4′-diglycidyldiphenylamine and 4,4′-diglycidyldibenzyl-methylamine; diglycidylamino compounds such as diglycidylaniline, N, N′-diglycidyl-4-glycidyloxyaniline, diglycidylorthotoluidine, tetraglycidylmetaxylene diamine, tetraglycidylaminodiphenylmethane, tetraglycidyl-p-phenylenediamine, diglycidylaminomethylcyclohexane and tetraglycidyl-1,3-bisaminomethyl cyclohexane; amino group-containing acid chlorides such as bis-(1-methylpropyl) carbamate chloride, 4-morpholincarbonyl chloride, 1-pyrrolidincarbonyl chloride, N, N-dimethylcarbamate chloride and N, N-diethylcarbamate chloride; epoxy group-containing silane compounds such as 1,3-bis-(glycidyloxypropyl)tetramethyldisiloxane and (3-glycidyloxypropyl)-pentamethyldisiloxane; sulfide group-containing silane compounds such as (trimethylsilyl) [3-(trimethoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(triethoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(tripropoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(tributoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(methyldimethoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(methyldiethoxysilyl) propyl] sulfide, (trimethylsilyl) [3-(methyldipropoxysilyl) propyl] sulfide, and (trimethylsilyl) [3-(methyldibutoxysilyl) propyl] sulfide; N-substituted aziridine compound such as ethyleneimine and propyleneimine; alkoxysilanes such as methyltriethoxy silane, N, N-bis (trimethylsilyl)-3-aminopropyltrimethoxysilane, N, N-bis (trimethylsilyl)-3-aminopropyltriethoxysilane, N, N-bis (trimethylsilyl) aminoethyltrimethoxysilane and N, N-bis (trimethylsilyl) aminoethyltriethoxysilane; (thio) benzophenone compounds having an amino group and/or a substituted amino group such as 4-N, N-dimethylaminobenzophenone, 4-N, N-di-t-butylaminobenzophenone, 4-N, N-diphenylamino benzophenone, 4,4′-bis (dimethylamino) benzophenone, 4,4′-bis (diethylamino) benzophenone, 4,4′-bis (diphenylamino) benzophenone and N, N, N′, N′-bis-(tetraethylamino) benzophenone; benzaldehyde compounds having an amino group and/or a substituted amino group such as 4-N, N-dimethylaminobenzaldehyde, 4-N, N-diphenylaminobenzaldehyde and 4-N, N-divinylamino benzaldehyde; N-substituted pyrrolidone such as N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, N-phenyl-2-pyrrolidone, N-t-butyl-2-pyrrolidone and N-methyl-5-methyl-2-pyrrolidone N-substituted piperidone such as N-methyl-2-piperidone, N-vinyl-2-piperidone and N-phenyl-2-piperidone; and N-substituted lactams such as N-methyl-ε-caprolactam, N-phenyl-ε-caprolactam, N-methyl-ω-laurilolactam, N-vinyl-ω-laurillolactam, N-methyl-β-propiolactam and N-phenyl-β-propiolactam. In addition to the above, N, N-bis-(2,3-epoxypropoxy)-aniline, 4,4-methylene-bis-(N, N-glycidyl-aniline), tris-(2,3-epoxypropyl)-1,3,5-triazine-2,4,6-triones, N,N-diethylacetamide, N-methylmaleimide, N, N-diethylurea, 1,3-dimethylethyleneurea, 1,3-divinylethyleneurea, 1,3-diethyl-2-imidazolidinone, 1-methyl-3-ethyl-2-imidazolidinone, 4-N,N-dimethylaminoacetophen, 4-N,N-diethylaminoacetophenone, 1,3-bis (diphenylamino)-2-propanone, 1,7-bis (methylethylamino)-4-heptanone, and the like can be mentioned also. The modification with the above compound (modifier) can be carried out by a known method.

As the SBR, for example, SBR manufactured and sold by Sumitomo Chemical Co., Ltd., JSR Corporation, Asahi Kasei Corporation, Zeon Corporation, Versalis, etc. can be used. The SBR may be used alone or in combination of two or more.

(B) BR

The rubber composition may further contain BR, if necessary. In this case, the content of BR in 100 parts by mass of the rubber component is, for example, preferably more than 2 parts by mass, and more preferably more than 4 parts by mass. On the other hand, it is preferably less than 20 parts by mass, more preferably less than 10 parts by mass, and further more preferably less than 6 parts by mass.

The weight average molecular weight of BR is, for example, more than 100,000 and less than 2 million. The vinyl bond amount of BR is, for example, more than 1% by mass and less than 30% by mass. The cis content of BR is, for example, more than 1% by mass and less than 98% by mass. The trans content of BR is, for example, more than 1% by mass and less than 60% by mass.

The BR is not particularly limited, and BR having a high cis content (cis content of 90% or more), BR having a low cis content, BR containing syndiotactic polybutadiene crystals, and the like can be used. The BR may be either a non-modified BR or a modified BR. Examples of the modified BR include a modified BR into which the above-mentioned functional group has been introduced. These may be used alone or in combination of two or more. The cis content can be measured by infrared absorption spectrum analysis.

As the modified BR, for example, tin-modified BR can also be used. Tin-modified BR is obtained by polymerizing 1,3-butadiene with a lithium initiator followed by adding a tin compound. A tin-modified BR in which the terminal is further bonded by a tin-carbon bond is preferable.

Examples of the lithium initiator include lithium-based compounds such as alkyllithium, aryllithium, vinyllithium, organic tin lithium and organic nitrogen lithium compounds; and lithium metals. By using the lithium initiator as an initiator for tin-modified BR, a tin-modified BR having a high vinyl content and a low cis content can be produced.

Examples of tin compounds include tin tetrachloride, butyltin trichloride, dibutyltin dichloride, dioctyltin dichloride, tributyltin chloride, triphenyltin chloride, diphenyldibutyltin, triphenyltinethoxydo, diphenyldimethyltin, ditrilstin chloride, diphenyltin dioctanoate, divinyldiethyltin, tetrabenzyltin, dibutyltin distearate, tetraallyltin and p-tributyltin styrene.

The content of tin atoms in the tin-modified BR is preferably 50 ppm or more, and more preferably 60 ppm or more. On the other hand, it is preferably 3000 ppm or less, more preferably 2500 ppm or less, and further preferably 250 ppm or less.

The molecular weight distribution (Mw/Mn) of the tin-modified BR is preferably 2 or less, and more preferably 1.5 or less.

The vinyl bond amount of the tin-modified BR is preferably 5% by mass or more, and more preferably 7% by mass or more. On the other hand, the vinyl bond amount of the tin-modified BR is preferably 50% by mass or less, and more preferably 20% by mass or less.

The modified BR and the tin-modified BR described above may be used alone or in combination of two or more.

As the BR, for example, products of Ube Industries, Ltd., JSR Corporation, Asahi Kasei Corporation, and Nippon Zeon Corporation can be used.

(C) Isoprene Rubber

In addition, the rubber composition may further contain isoprene-based rubber, if necessary. In this case, the content of the isoprene-based rubber in 100 parts by mass of the rubber component is, for example, preferably more than 2 parts by mass, and more preferably more than 4 parts by mass. On the other hand, it is preferably less than 40 parts by mass, more preferably less than 20 parts by mass, and further more preferably less than 8 parts by mass.

Examples of the isoprene-based rubber include natural rubber (NR), isoprene rubber (IR), modified NR, modified NR and modified IR. From the viewpoint of excellent in strength, NR is preferable.

As the NR, those which are common in the tire industry, for example, SIR20, RSS #3, TSR20 and the like, can be used. The IR is not particularly limited, and those which are common in the tire industry, for example, IR 2200 or the like, can be used. Examples of the modified NR includes deproteinized natural rubber (DPNR), high-purity natural rubber (UPNR), and the like. Examples of the modified NR includes epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), grafted natural rubber, and the like. Examples of the modified IR include epoxidized isoprene rubber, hydrogenated isoprene rubber, and grafted isoprene rubber, and the like. These may be used alone or in combination of two or more.

(D) Other Rubber Components

Further, as the other rubber component, if necessary, rubber (polymer) generally used in the production of tires such as nitrile rubber (NBR) may be contained.

(b) Compounding Materials Other than Rubber Components

(A) Filler

In the present embodiment, the rubber composition preferably contains a filler. Specific examples of the filler include carbon black, silica, graphite, calcium carbonate, talc, alumina, clay, aluminum hydroxide and mica. Among them, silica can be preferably used as a reinforcing agent. In this case, it is preferable to be used in combination with a silane coupling agent. It is also preferable to use carbon black as a reinforcing agent, if necessary.

(i) Silica

The rubber composition preferably contains silica. The BET specific surface area of silica is preferably more than 140 m²/g, more preferably more than 160 m²/g, from the viewpoint of obtaining good durability performance. On the other hand, from the viewpoint of obtaining excellent low rolling resistance, it is preferably less than 250 m²/g, and more preferably less than 220 m²/g. The above-mentioned BET specific surface area is a value of N₂SA measured by the BET method according to ASTM D3037-93.

The content of silica with respect to 100 parts by mass of the rubber component is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, and further preferably 45 parts by mass or more. On the other hand, it is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, further preferably 100 parts by mass or less, further more preferably 80 parts by mass or less, still further more preferably 60 parts by mass or less, and particularly preferably 55 parts by mass or less.

Examples of silica include dry silica (anhydrous silica) and wet silica (hydrous silica). Of these, wet silica is preferable because it has a large number of silanol groups.

As commercially available products, for example, products of Degussa, Rhodia, Tosoh Silica Co., Ltd., Solvay Japan Co., Ltd., and Tokuyama Corporation can be used.

(ii) Silane Coupling Agent

As described above, when using silica, it is preferable to use a silane coupling agent in combination. The silane coupling agent is not particularly limited, and examples thereof include

sulfide type such as bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl)) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyltetrasulfide and 3-triethoxysilylpropyl ethacrylate monosulfide; mercapto type such as 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane and NXT and NXT-Z manufactured by Momentive; vinyl type such as vinyl triethoxysilane and vinyl trimethoxysilane; amino type such as 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; glycidoxy type such as γ-glycidoxypropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane; nitro-based such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; and chloro-based such as 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane. These may be used alone or in combination of two or more.

As the silane coupling agent, for example, products of Degussa, Momentive, Shinetsu Silicone Co., Ltd., Tokyo Chemical Industry Co., Ltd., Azumax Co., Ltd., or Toray Dow Corning Co., Ltd. can be used.

The content of the silane coupling agent is, for example, preferably more than 3 parts by mass, more preferably more than 5 parts by mass, further preferably more than 7 parts by mass, and further more preferably more than 9 parts by mass with respect to 100 parts by mass of silica. On the other hand, it is preferably less than 15 parts by mass, more preferably less than 13 parts by mass, and further more preferably less than 11 parts by mass.

(iii) Carbon Black

The rubber composition preferably contains carbon black, if necessary. The content of carbon black is, for example, preferably 2 parts by mass or more, and more preferably 3 parts by mass or more with respect to 100 parts by mass of the rubber component. On the other hand, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and further preferably 5 parts by mass or less.

The carbon black is not particularly limited, and furnace black (furness carbon black) such as SAF, ISAF, HAF, MAF, FEF, SRF, GPF, APF, FF, CF, SCF and ECF; acetylene black (acetylene carbon black); thermal black (thermal carbon black) such as FT and MT; channel black (channel carbon black) such as EPC, MPC and CC, and the like can be used. These may be used alone or in combination of two or more.

Nitrogen adsorption specific surface area of the carbon black (N₂SA) is, for example, more than 30 m²/g and less than 250 m²/g. The amount of dibutyl phthalate (DBP) absorbed by carbon black is, for example, more than 50 ml/100 g and less than 250 ml/100 g. The nitrogen adsorption specific surface area of carbon black is measured according to ASTM D4820-93, and the amount of DBP absorbed is measured according to ASTM D2414-93.

Specific examples of carbon black are not particularly limited, and examples thereof include N134, N110, N220, N234, N219, N339, N330, N326, N351, N550, and N762. Commercially available products include, for example, product of Asahi Carbon Co., Ltd., Cabot Japan Co., Ltd., Tokai Carbon Co., Ltd., Mitsubishi Chemical Corporation, Lion Corporation, Shin Nikka Carbon Co., Ltd., Columbia Carbon Co., Ltd., or the like can be used. These may be used alone or in combination of two or more.

(iv) Other Fillers

In addition to the above-mentioned silica and carbon black, the rubber composition may further contain fillers generally used in the tire industry, such as calcium carbonate, talc, alumina, clay, aluminum hydroxide, mica, graphite and the like. These contents are, for example, more than 0.1 parts by mass and less than 200 parts by mass with respect to 100 parts by mass of the rubber component.

(B) Curable Resin Component

The rubber composition may contain a curable resin component such as a modified resorcin resin, a modified phenol resin or the like, if necessary. It is considered that this makes it possible to increase the rigidity of the rubber composition and obtain good steering stability during high-speed driving.

Specific examples of the modified resorcin resin include Sumikanol 620 (modified resorcin resin) manufactured by Taoka Chemical Industry Co., Ltd., and examples of the modified phenol resin include PR12686 (cashew oil modified phenolic resin) manufactured by Sumitomo Bakelite Co., Ltd.

The content of the curable resin component is preferably 1 part by mass or more, and more preferably 2 parts by mass or more, with respect to 100 parts by mass of the rubber component, for example, from the viewpoint of sufficiently improving the complex elastic modulus. On the other hand, from the viewpoint of maintaining the breaking strength, it is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less.

When using the modified resorcin resin, it is preferable to also contain a methylene donor as a curing agent. Examples of the methylene donor include hexamethylenetetramine (HMT), hexamethoxymethylol melamine (HMMM) and hexamethylol melamine pentamethyl ether (HMMPME). It is preferably contained in an amount of 5 parts by mass or more and about 15 parts by mass, with respect to 100 parts by mass of the curable resin component. If it is too small, a sufficient complex elastic modulus may not be obtained. On the other hand, if the amount is too large, the viscosity of the rubber may increase and the workability may deteriorate.

As a specific methylene donor, for example, Sumikanol 507 manufactured by Taoka Chemical Industry Co., Ltd. can be used.

(C) Plasticizer Component

The rubber composition may contain a plasticizer component such as an oil (including a spreading oil), a liquid polymer and a resin, as a component for softening the rubber. The plasticizer component is a component that can be extracted from the vulcanized rubber with acetone. The total content of the plasticizer component is preferably more than 5 parts by mass and more preferably more than 10 parts by mass with respect to 100 parts by mass of the rubber component. On the other hand, it is preferably less than 70 parts by mass, more preferably less than 50 parts by mass, and further more preferably less than 30 parts by mass. The amount of oil contained in the rubber (oil-extended rubber) is also included in this plasticizer component.

(i) Oil

Examples of the oil include mineral oil (generally referred to as process oil), vegetable oil and fat, and a mixture thereof. As the mineral oil (process oil), for example, paraffin-based process oil, aroma-based process oil, naphthen-based process oil and the like can be used. Examples of vegetable oils and fats include castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, peanut oil, rosin, pine oil, pine tar, tall oil, corn oil, rice oil, beni flower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, camellia oil, jojoba oil, macadamia nut oil, and tung oil. These may be used alone or in combination of two or more.

Specific examples of process oils (mineral oils) include products of Idemitsu Kosan Co., Ltd., Sankyo Yuka Kogyo Co., Ltd., Japan Energy Co., Ltd., Orisoi Co., Ltd., H & R Co., Ltd., Toyokuni Oil Co., Ltd., Showa Shell Sekiyu Co., Ltd., Fuji Kosan Co., Ltd. and the like can be used.

(ii) Liquid Rubber

The liquid rubber mentioned as a plasticizer is a polymer in a liquid state at room temperature (25° C.), and is a rubber component that can be extracted from a tire after vulcanization by acetone extraction. Examples of the liquid rubber include farnesene-based polymers, liquid diene-based polymers, and hydrogenated compounds thereof.

The farnesene-based polymer is a polymer obtained by polymerizing farnesene, and has a structural unit based on farnesene. In farnesene, isomers such as α-farnesene ((3E,7E)-3,7,11-trimethyl-1,3,6,10-dodecatetraene) and β-farnesene (7,11-dimethyl-3-methylene-1, 6,10-dodecatriene), are present.

The farnesene-based polymer may be a homopolymer of farnesene (farnesene homopolymer) or a copolymer of farnesene and a vinyl monomer (farnesene-vinyl monomer copolymer).

Examples of the liquid diene polymer include a liquid styrene-butadiene copolymer (liquid SBR), a liquid butadiene polymer (liquid BR), a liquid isoprene polymer (liquid IR), and a liquid styrene isoprene copolymer (liquid SIR).

Liquid diene polymer has a weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC) (Mw) is, for example, more than 1.0×10³, and less than 2.0×10⁵. In the present specification, Mw of the liquid diene polymer is a value measured by gel permeation chromatography (GPC) in terms of polystyrene.

The content of the liquid rubber (total content of the liquid farnesene polymer, the liquid diene polymer, etc.) is, for example, more than 1 part by mass and less than 100 parts by mass with respect to 100 parts by mass of the rubber component.

As the liquid rubber, for example, products of Kuraray Co., Ltd. and Clay Valley Co., Ltd. can be used.

(iii) Resin Component

The resin component also functions as an adhesive-imparting component and may be solid or liquid at room temperature. Specific examples of the resin components include rosin-based resin, styrene-based resin, and cumarone-based resin, terpene-based resin, C5 resin, C9 resin, C5C9 resin, and acrylic resin, and two or more kinds may be used in combination. The content of the resin component is preferably more than 2 parts by mass, and less than 45 parts by mass with respect to 100 parts by mass of the rubber component, and more preferably less than 30 parts by mass.

The rosin-based resin is a resin containing rosin acid as a main component, which is obtained by processing pine fat. This rosin-based resin (rosins) can be classified according to the presence or absence of modification, and can be classified into non-modified rosin (unmodified rosin) and rosin modified product (rosin derivative). Non-modified rosins include tall rosins (also known as tall oil rosins), gum rosins, wood rosins, asymmetric rosins, polymerized rosins, hydrogenated rosins, and other chemically modified rosins. The rosin-modified product is a modified product of non-modified rosin, and examples thereof include rosin esters, unsaturated carboxylic acid-modified rosins, unsaturated carboxylic acid-modified rosin esters, rosin amide compounds, and amine salts of rosin.

The styrene-based resin is a polymer using a styrene-based monomer as a constituent monomer, and examples thereof include a polymer obtained by polymerizing a styrene-based monomer as a main component (50% by mass or more). Specifically, a homopolymer obtained by independently polymerizing styrene-based monomers, such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene and p-chlorostyrene, a copolymer obtained by copolymerizing two or more types of styrene-based monomers, and a copolymer obtained by copolymerizing a styrene-based monomer and another monomer that can be copolymerized with the styrene-based monomer.

Examples of the other monomer include acrylonitriles such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; unsaturated carboxylic acid esters such as methyl acrylate and methyl methacrylate; dienes such as chloroprene, butadiene and isoprene; olefins such as 1-butene and 1-pentene; and α, β-unsaturated carboxylic acids and acid anhydrides thereof such as maleic anhydride.

Among the cumarone-based resins, the cumarone indene resin is preferable. The cumarone indene resin is a resin containing cumarone and indene as monomer components constituting the skeleton (main chain) of the resin. Examples of the monomer component contained in the skeleton other than cumarone and indene include styrene, α-methylstyrene, methylindene, vinyltoluene and the like.

The content of the cumarone indene resin is, for example, more than 1.0 part by mass and less than 50.0 parts by mass with respect to 100 parts by mass of the rubber component.

The hydroxyl value (OH value) of the cumarone indene resin is, for example, more than 15 mgKOH/g and less than 150 mgKOH/g. The OH value is the amount of potassium hydroxide required to neutralize acetic acid bonded to a hydroxyl group when acetylating 1 g of the resin, and is expressed in milligrams. The OH value is a value measured by a potentiometric titration (JIS K 0070: 1992).

The softening point of the cumarone indene resin is, for example, more than 30° C. and less than 160° C. The softening point is the temperature at which the ball drops when the softening point defined in JIS K 6220-1: 2001 is measured by a ring-ball type softening point measuring device.

Examples of the terpene-based resin include polyterpenes, terpene phenols, and aromatic-modified terpene resins. Polyterpenes are resins obtained by polymerizing terpene compounds, and their hydrogenated products. Terpene compounds are hydrocarbons represented by a composition of (C₅ H₈)n and their oxygenated derivatives, and are compounds having a terpene, classified in monoterpenes (C₁₀H₁₆), sesquiterpene (C₁₅H₂₄), diterpenes (C₂₀H₃₂), etc., as a basic skeleton. Examples thereof include α-pinene, β-pinene, dipentene, limonene, myrcene, aloossimen, ocimene, α-phellandrene, α-terpinene, γ-terpinene, terpinolene, 1,8-cineol, 1,4-cineol, α-terpineol, β-terpineol, and γ-terpineol.

Examples of the polyterpene include terpene resins, such as α-pinene resin, β-pinene resin, limonene resin, dipentene resin, and β-pinene/limonene resin, made from the above-mentioned terpene compound, and hydrogenated terpene resin obtained by hydrogenating the terpene resin can also be mentioned as an example. Examples of the terpene phenol include a resin obtained by copolymerizing the above-mentioned terpene compound and a phenol-based compound, and a resin obtained by hydrogenating the resin. Specifically, a resin obtained by condensing the above-mentioned terpene compound, phenolic compound and the formalin can be mentioned. Examples of the phenolic compound include phenol, bisphenol A, cresol, xylenol and the like. Examples of the aromatic-modified terpene resin include a resin obtained by modifying the terpene resin with an aromatic compound, and a resin obtained by hydrogenating the resin. The aromatic compound is not particularly limited as long as it has an aromatic ring, but for example, phenol compounds such as phenol, alkylphenol, alkoxyphenol, and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol, and unsaturated hydrocarbon group-containing naphthol; styrene derivatives such as styrene, alkylstyrene, alkoxystyrene, and unsaturated hydrocarbon group-containing styrene; cumarone; inden; and the like can be mentioned.

The “C5 resin” refers to a resin obtained by polymerizing a C5 fraction. Examples of the C5 fraction include petroleum fractions having 4 to 5 carbon atoms equivalent to cyclopentadiene, pentene, pentadiene, isoprene, and the like. As the C5 petroleum resin, a dicyclopentadiene resin (DCPD resin) is preferably used.

The “C9 resin” refers to a resin obtained by polymerizing a C9 fraction, and may be hydrogenated or modified. Examples of the C9 fraction include petroleum fractions having 8 to 10 carbon atoms equivalent to vinyltoluene, alkylstyrene, indene, methyl indene and the like. As a specific example, a cumarone indene resin, a cumarone resin, an indene resin, and an aromatic vinyl-based resin are preferably used. As the aromatic vinyl resin, a homopolymer of α-methylstyrene or styrene or a copolymer of α-methylstyrene and styrene is preferable because it is economical, easy to process, and has excellent heat generation. A copolymer of α-methylstyrene and styrene is more preferable. As the aromatic vinyl resin, for example, those commercially available from Clayton, Eastman Chemical, etc. can be used.

The “C5C9 resin” refers to a resin obtained by copolymerizing the C5 fraction and the C9 fraction, and may be hydrogenated or modified. Examples of the C5 fraction and the C9 fraction include the above-mentioned petroleum fraction. As the C5C9 resin, for example, those commercially available from Tosoh Corporation, LUHUA, etc. can be used.

The acrylic resin is not particularly limited. For example, a solvent-free acrylic resin can be used.

As the solvent-free acrylic resin, a (meth) acrylic resin (polymer), synthesized by a high-temperature continuous polymerization method (high-temperature continuous lump polymerization method) described in U.S. Pat. No. 4,414,370, JP-A-S59-6207, JP-B-H5-58005, JP-A-H1-313522, U.S. Pat. No. 5,010,166, Toagosei Annual Report TREND2000 No. 3, pp 42-45, etc. without using polymerization initiators, chain transfer agents, organic solvents, etc. as auxiliary raw materials as much as possible, can be mentioned. Note that, “(meth) acrylic” means meth acrylic and acrylic.

Examples of the monomer component constituting the acrylic resin include (meta) acrylic acid derivatives such as (meth) acrylic acid, (meth) acrylic acid ester (alkyl ester, aryl ester, aralkyl ester, etc.), (meth) acrylamide, and (meth) acrylamide derivative.

As the monomer component constituting the acrylic resin, styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene, divinylbenzene, trivinylbenzene, divinylnaphthalene, and the like can be used, together with (meth) acrylic acid and/or (meth) acrylic acid derivative.

The acrylic resin may be a resin composed of only a (meth) acrylic component or a resin also having a component other than the (meth) acrylic component as a component. The said acrylic resin may have a hydroxyl group, a carboxyl group, a silanol group or the like.

As the resin component, for example, products of Maruzen Petrochemical Co., Ltd., Sumitomo Bakelite Co., Ltd., Yasuhara Chemical Co., Ltd., Toso Co., Ltd., Rutgers Chemicals Co., Ltd., BASF, Arizona Chemical Co., Ltd., Nitto Chemical Co., Ltd., Co., Ltd, Nippon Catalyst, JX Energy Co., Ltd., Arakawa Chemical Industry Co., Ltd., or Taoka Chemical Industry Co., Ltd. can be used.

(D) Anti-Aging Agent

The rubber composition preferably contains an anti-aging agent. The content of the anti-aging agent is, for example, more than 1 part by mass and less than 10 parts by mass with respect to 100 parts by mass of the rubber component.

Examples of the anti-aging agent include naphthylamine-based anti-aging agents such as phenyl-α-naphthylamine; diphenylamine-based anti-aging agents such as octylated diphenylamine and 4,4′-bis (α, α′-dimethylbenzyl) diphenylamine; p-phenylenediamine-based anti-aging agent such as N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, and N, N′-di-2-naphthyl-p-phenylenediamine; quinoline-based anti-aging agent such as a polymer of 2,2,4-trimethyl-1,2-dihydroquinolin; monophenolic anti-aging agents such as 2,6-di-t-butyl-4-methylphenol, and styrenated phenol; and bis, tris, polyphenolic anti-aging agent such as tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane. These may be used alone or in combination of two or more.

As the anti-aging agent, for example, products of Seiko Chemical Co., Ltd., Sumitomo Chemical Co., Ltd., Ouchi Shinko Chemical Industry Co., Ltd., Flexis Co., Ltd., etc. can be used.

(E) Stearic Acid

The rubber composition may contain stearic acid. The content of stearic acid is, for example, more than 0.5 parts by mass and less than 10.0 parts by mass with respect to 100 parts by mass of the rubber component. As the stearic acid, conventionally known ones can be used, and for example, products of NOF Corporation, Kao Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., or Chiba Fatty Acid Co., Ltd. can be used.

(F) Zinc Oxide

The rubber composition may contain zinc oxide. The content of zinc oxide is, for example, more than 0.5 parts by mass and less than 15 parts by mass with respect to 100 parts by mass of the rubber component. Conventionally known zinc oxide can be used. For example, products of Mitsui Metal Mining Co., Ltd., Toho Zinc Co., Ltd., HakusuiTech Co., Ltd., Shodo Chemical Industry Co., Ltd., Sakai Chemical Industry Co., Ltd., etc. can be used.

(G) Cross-Linking Agent and Vulcanization Accelerator

The rubber composition preferably contains a cross-linking agent such as sulfur. The content of the cross-linking agent is, for example, more than 0.1 part by mass and less than 10.0 parts by mass with respect to 100 parts by mass of the rubber component.

Examples of sulfur include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and soluble sulfur, which are commonly used in the rubber industry. These may be used alone or in combination of two or more.

As the sulfur, for example, products of Tsurumi Chemical Industry Co., Ltd., Karuizawa Sulfur Co., Ltd., Shikoku Chemicals Corporation, Flexis Co., Ltd., Nippon Kanryu Industry Co., Ltd., Hosoi Chemical Industry Co., Ltd., etc. can be used.

Examples of the cross-linking agent other than sulfur include a vulcanizing agent containing a sulfur atom such as Tackylol V200 manufactured by Taoka Chemical Industry Co., Ltd., Duralink HTS (1,6-hexamethylene-sodium dithiosulfate dihydrate) manufactured by Flexis, and KA9188 (1,6-bis (N, N′-dibenzylthiocarbamoyldithio) hexane) manufactured by Lanxess; and an organic peroxide such as dicumyl peroxide.

The rubber composition preferably contains a vulcanization accelerator. The content of the vulcanization accelerator is, for example, more than 0.3 parts by mass and less than 10.0 parts by mass with respect to 100 parts by mass of the rubber component.

Examples of the vulcanization accelerator include thiazole-based vulcanization accelerator such as 2-mercaptobenzothiazole, di-2-benzothiazolyldisulfide, and N-cyclohexyl-2-benzothiazylsulfenamide; thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide (TMTD), tetrabenzyl thiuram disulfide (TBzTD), and tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N);

sulfenamide-based vulcanization accelerators such as N-cyclohexyl-2-benzothiazolesulfenamide, N-t-butyl-2-benzothiazolyl sulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, N-oxyethylene-2-benzothiazolesulfenamide, and N, N′-diisopropyl-2-benzothiazolesulfenamide; and guanidine-based vulcanization accelerators such as diphenylguanidine, dioltotrilguanidine, and orthotrilbiguanidine can be mentioned. These may be used alone or in combination of two or more.

(H) Other

In addition to the above components, the rubber composition may further blend additives commonly used in the tire industry, such as fatty acid metal salts, carboxylic acid metal salts, organic peroxides, reversion (vulcanization return) inhibitors, and the like. The content of these additives is, for example, more than 0.1 parts by mass and less than 200 parts by mass with respect to 100 parts by mass of the rubber component.

(2) Preparation of Rubber Composition

The rubber composition is produced by a general method, for example, by a manufacturing method including a base kneading step of kneading a rubber component with a filler such as silica or carbon black, and a finish kneading step of kneading the kneaded product obtained in the base kneading step and a cross-linking agent.

The kneading can be performed using, for example, a known (sealed) kneader such as a Banbury mixer, a kneader, or an open roll.

The kneading temperature of the base kneading step is, for example, more than 50° C. and less than 200° C., and the kneading time is, for example, more than 30 seconds and less than 30 minutes. In the base kneading step, in addition to the above components, compounding agents conventionally used in the rubber industry, such as softeners such as oil, stearic acid, zinc oxide, antiaging agents, waxes, vulcanization accelerators, etc., may be appropriately added and knead as needed.

In the finish kneading step, the kneaded product obtained in the base kneading step and the cross-linking agent are kneaded. The kneading temperature in the finish kneading step is, for example, more than room temperature and less than 80° C., and the kneading time is, for example, more than 1 minute and less than 15 minutes. In the finish kneading step, in addition to the above components, a vulcanization accelerator, zinc oxide and the like may be appropriately added and kneaded as needed.

(3) Manufacture of Tread Portion

The tread portion can be manufactured by molding the rubber composition obtained above into a predetermined shape. In the case of a multi-layered tread such as a cap layer and a base layer, the above rubber composition is used as the outermost layer.

2. Manufacture of Belt Members

The belt member can be manufactured by topping a known coating rubber composition for coating on both sides of a reinforcing cord (monofilament cord such as a steel cord) arranged (50 lines/5 cm or more) in parallel at predetermined intervals.

3. Tire Manufacturing

The tire of the present invention can be produced as an unvulcanized tire by molding the tread portion and the belt member obtained above together with other tire members by a usual method on a tire molding machine.

Specifically, the inner liner as a member to ensure the airtightness of the tire, the carcass as a member to withstand the load, impact and filling air pressure received by the tire, a belt member as a member to strongly tighten the carcass to increase the rigidity of the tread, and the like are wound on a molded drum, then both ends of the carcass are fixed to both side edges and a bead part as a member for fixing the tire to the rim is arranged to form a toroid shape, followed by pasting a tread to the central portion of the outer circumference and a sidewall to the outer side in the radial direction to form a side portion; and an unvulcanized tire is manufactured.

In the present embodiment, as described above, it is preferable that at least two belt layers are provided to form the belt member from the viewpoint of increasing the restraint force on the driving tread and facilitating the suppression of the growth of the outer diameter. At this time, in the vulcanized tire, the average distance D (mm) between the belt layers in the tread portion is preferably 0.6 mm or less. Further, it is also preferable that the angle formed by the respective belt layers in the tire circumferential direction in the tread portions is 65° or less.

The angle of the steel cord is the angle of the steel cord with respect to the tire circumferential direction when the tire is not filled with air, and can be confirmed by peeling the tread portion from the outside in the radial direction of the tire.

Then, the produced unvulcanized tire is heated and pressurized in a vulcanizer to obtain a tire. The vulcanization step can be carried out by applying a known vulcanization means. The vulcanization temperature is, for example, more than 120° C. and less than 200° C., and the vulcanization time is, for example, more than 5 minutes and less than 15 minutes.

It is preferable that the tire cross-sectional width Wt (mm) and tire outer diameter Dt (mm), when the tire is assembled to a regular rim and has the internal pressure of 250 kPa, satisfy the following formula, since excellent low rolling resistance can be attained.

1600≤(Dt ²×π/4)/Wt≤2827.4

As specific tires to which the present invention is preferably applied, tires with the size of 145/60R18, 145/60R19, 155/55R18, 155/55R19, 155/70R17, 155/70R19, 165/55R20, 165/55R21,165/60R19, 165/65R19, 165/70R18, 175/55R19, 175/55R20, 175/55R22, 175/60R18, 185/55R19, 185/60R20, 195/50R20, and 195/55R20 can be mentioned.

Among the tires classified into passenger car tires, truck/bus tires, motorcycle tires, etc., the present embodiment is preferably applied to a passenger car tire, that is, a tire mounted on an automobile driving on four wheels and having the maximum load capacity of 1000 kg or less, and the tires can contribute more favorably for solving the problem in the present invention of providing a pneumatic tire having excellent steering stability and durability at high-speed driving by satisfying (formula 1).

The above-mentioned maximum load capacity is not particularly limited as long as it is 1000 kg or less, but generally, as the maximum load capacity increases, the tire weight tends to increase and the impact transmitted to the tire tends to increase. Therefore, the maximum load capacity is preferably 900 kg or less, more preferably 800 kg or less, and further preferably 700 kg or less.

Here, the tire weight is preferably 20 kg or less, more preferably 15 kg or less, and further preferably 12 kg or less, 10 kg or less and 8 kg or less from the viewpoint of softening the impact transmitted to the tire.

Examples

Hereinafter, the present invention will be described in more detail with reference to Examples.

Experiment 1

In this experiment, tires with a tire size of 185/65R16 were prepared and evaluated.

1. Manufacture of Rubber Compositions for Tread

First, a rubber composition for tread was produced.

(1) Compounding Material

First, each compounding material shown below was prepared.

(a) Rubber Component (A) NR: TSR20

(B) SBR: C2525 (Solution Polymerization SBR) manufactured by Versalis

(Styrene content: 26% by mass, vinyl bond amount: 24% by mass)

(C) BR: UBEPOL BR150B manufactured by Ube Industries, Ltd.

(cis content: 97% by mass, trans content: 2% by mass)

(b) Compounding Materials Other than Rubber Components (A) Carbon Black: Show Black N220 manufactured by Cabot Japan Co., Ltd.

-   -   (N₂SA: 111 m²/g)         (B) Silica: Ultrasil VN3 manufactured by Evonik Industries, Inc.     -   (BET specific surface area: 165 m²/g)         (C) Silane coupling agent: Si69 manufactured by Degusa     -   (Bis (3-triethoxysilylpropyl) tetrasulfide)         (D) Oil: VIVATEC NC500 manufactured by H & R (aroma-based         process oil)         (E) Resin: Terpene styrene resin TO125 manufactured by Yasuhara         Chemical Co., Ltd. (Aromatic modified terpene resin)         (F) Zinc oxide: Zinc Oxide No. 1 manufactured by Mitsui Mining &         Smelting Co., Ltd.         (G) Anti-aging agent-1: Nocrack 6C manufactured by Ouchi Shinko         Kagaku Kogyo Co., Ltd.

(N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine)

(H) Anti-aging agent-2: Antage RD manufactured by Kawaguchi Chemical Industry Co., Ltd. (2,2,4-trimethyl-1,2-dihydroquinoline) (I) Wax: Ozo Ace 0355 manufactured by Nippon Seiro Co., Ltd. (J) Stearic acid: Stearic acid “Tsubaki” manufactured by NOF CORPORATION (K) Cross-linking agent and vulcanization accelerator

Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd.

Vulcanization accelerator-1: Noxeller CZ-G (CZ) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

-   -   (N-cyclohexyl-2-benzothiazolyl sulfeneamide)

Vulcanization accelerator-2: Noxeller D (DPG) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

-   -   (1,3-Diphenylguanidine)

(2) Production of Rubber Composition

Materials other than sulfur and the vulcanization accelerator were kneaded under the conditions of 150° C. for 5 minutes using a Banbury mixer according to the respective blending contents shown in Tables 1 and 2, to obtain a kneaded product. Each compounding amount is a mass part.

Next, sulfur and a vulcanization accelerator were added to the obtained kneaded product, and the mixture was kneaded using an open roll for 5 minutes under the condition of 80° C. to obtain a rubber composition for tread.

2. Tire Manufacturing

First, the steel cords having the configurations and outer diameters shown in Tables 1 and 2 were arranged with the ends (lines/5 cm) shown in Tables 1 and 2, and then the previously obtained rubber composition for belt was applied to both sides thereof. A belt member having a total thickness of “cord diameter (mm)+distance between cords×2 (mm)” was produced.

After that, two layers of belt members were laminated to form a belt layer so as to intersect each other at the distances and angles shown in Tables 1 and 2, then the belt layer, a tread member produced by using the above-mentioned rubber composition for tread, and other tire members were laminated to form an unvulcanized tire, which was then vulcanized for 10 minutes under the condition of 170° C. to produce each test tire shown in Table 1 and Table 2. (Outer diameter Dt: 646 mm, cross-sectional width Wt: 189 mm, Virtual volume V: 37429958 mm³).

In each test tire, the above-mentioned (L₈₀/L₀) is 0.5, the total cross-sectional area of the circumferential groove is 22% of the cross-sectional area of the tread portion, and the total volume of the lateral grooves including the lateral grooves in which the groove width/groove depth is 0.65 was 3.5% of the volume of the tread portion.

3. Parameter Calculation

After that, the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer of each test tire was measured, and the tire weight WT (kg) was measured, and the ratio of WT to the maximum load capacity WL (kg) calculated from the above V (WT/WL) was determined. At the same time, rubber was cut out from the belt layers of each test tire to prepare a rubber test piece for viscoelasticity measurement having a length of 40 mm and a width of 4 mm. Using the Iplexer series manufactured by GABO, the complex elastic modulus E*(MPa) was measured under the conditions of the temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, and deformation mode: elongation, and (E*×T) was determined. The results are shown in Tables 1 and 2.

4. Performance Evaluation Test (1) Evaluation of Steering Stability

After mounting each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc) and filling it with air so that the internal pressure became 250 kPa, the driver sensually inspected the handling property in 5 stages of from 1 to 5 when driving at the speed of 120 km/h on the test course on the dry road surface. Then, the total score of the evaluation by 20 drivers was calculated.

Next, the result in Comparative Example 1-10 was set to 100 and the evaluation was indexed based on the following formula to evaluate the steering stability during high-speed driving. The larger the value, the better the steering stability at high-speed driving.

Steering stability=[(Result of test tire)/(Result of Comparative Example 1-10)]×100

(2) Evaluation of Durability Performance

After mounting each test tire on all wheels of the vehicle (domestic FF vehicle, displacement 2000 cc) and filling it with air so that the internal pressure becomes 250 kPa, a driving 10 laps at a speed of 50 km/h, followed by climbing onto the unevenness provided on the road surface at a speed of 80 km/h was repeated on the test course on a dry road surface in an overloaded state. Thereafter, the lap was performed again at a speed of 50 km/h and then the speed was gradually increased to measure the speed at the time when the driver felt an abnormality.

Next, the result in Comparative Example 1-10 was set as 100, and the durability performance was relatively evaluated by indexing based on the following formula. The larger the value, the better the durability.

Durability=[(Result of test tire)/(Result of Comparative Example 1-10)]×100

(3) Comprehensive Evaluation

The evaluation results of (1) and (2) above were totaled to form a comprehensive evaluation.

(4) Evaluation Result

The results of each evaluation are shown in Tables 1 and 2. In Tables, “1×1” indicates a monofilament, and “1×2” indicates indicates a twisted cord in which two filaments are twisted together.

TABLE 1 Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 (Mixing) NR 5 5 5 5 5 5 5 5 5 SBR 90 90 90 90 90 90 90 90 90 BR 5 5 5 5 5 5 5 5 5 Carbon black 4 4 4 4 4 4 4 4 4 Silica 50 50 50 50 50 50 50 55 55 Silane coupling agent 5 5 5 5 5 5 5 5.5 5.5 Oil 20 20 20 20 20 20 20 20 10 Resin 25 25 25 25 25 25 25 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 Wax 1 1 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 55 55 55 55 55 75 90 75 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.45 0.22 0.45 0.45 0.45 0.45 Angle (°) 100 60 46 46 46 46 46 46 46 (Parameter) WT (kg) 6.9 6.8 6.9 6.8 6.7 6.9 7 6.9 6.8 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 512 512 512 512 512 512 512 512 512 WT/WL 0.0135 0.0133 0.0135 0.0133 0.0131 0.0135 0.0137 0.0135 0.0133 T (mm) 7.9 7.8 7.9 7.9 7.9 7.9 7.9 7.9 7.7 E* × T 27.7 27.3 27.7 27.7 27.7 27.7 27.7 37.1 42.4 (Evaluation result) Steering stability 103 107 110 115 118 120 123 125 128 Durability 110 112 118 125 115 119 122 125 133 Comprehensive 213 219 228 240 233 239 245 250 261 evaluation

TABLE 2 Comparative Example 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 1-10 (Mixing) NR 5 5 5 5 5 5 5 5 5 5 SBR 75 75 75 75 75 75 75 75 90 90 BR 20 20 20 20 20 20 20 20 5 5 Carbon black 4 4 4 4 4 4 4 4 4 4 Silica 55 55 55 55 55 55 55 55 55 55 Silane coupling agent 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 Oil 45 45 45 45 45 45 45 45 20 10 Resin 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 1 Wax 1 1 1 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 2 1 × 2 1 × 2 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.59 0.59 0.59 0.59 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 42 42 55 42 42 55 55 55 55 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.7 0.7 0.7 0.45 0.45 0.45 0.45 Angle (°) 100 100 100 100 100 100 100 60 60 60 (Parameter) WT (kg) 7.3 7 7.2 7.3 7.1 7.2 7.2 7.6 7.3 7.3 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 512 512 512 512 512 512 512 512 512 512 WT/WL 0.0143 0.0137 0.0141 0.0143 0.0139 0.0141 0.0141 0.0149 0.0143 0.0143 T (mm) 8.4 7.9 8.4 8.4 8.2 8.4 8.3 9.0 8.4 8.4 E* × T 29.4 27.7 29.4 29.4 28.7 29.4 29.1 31.5 39.5 46.2 (Evaluation result) Steering stability 85 83 88 85 82 88 93 90 84 100 Durability 90 84 93 86 81 92 89 90 97 100 Comprehensive 175 167 181 171 163 180 182 180 181 200 evaluation

Experiment 2

In this experiment, a tire having a tire size of 205/55R16 (outer diameter Dt: 632 mm, cross-sectional width Wt: 214 mm, virtual volume V: 39373809 mm³) was prepared and evaluated.

After manufacturing each of the test tires shown in Tables 3 and 4 in the same manner as in Experiment 1, each parameter was obtained in the same manner. Then, in the same manner, a performance evaluation test was conducted and evaluated. The steering stability was evaluated with the result in Comparative Example 2-10 as 100, and the durability performance was also evaluated with the result in Comparative Example 2-10 as 100. The results of each evaluation are shown in Tables 3 and 4.

TABLE 3 Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 (Mixing) NR 5 5 5 5 5 5 5 5 5 SBR 90 90 90 90 90 90 90 90 90 BR 5 5 5 5 5 5 5 5 5 Carbon black 4 4 4 4 4 4 4 4 4 Silica 50 50 50 50 50 50 50 55 55 Silane coupling agent 5 5 5 5 5 5 5 5.5 5.5 Oil 20 20 20 20 20 20 20 20 10 Resin 25 25 25 25 25 25 25 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 Wax 1 1 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 55 55 55 55 55 75 90 75 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.45 0.22 0.45 0.45 0.45 0.45 Angle (°) 100 60 46 46 46 46 46 46 46 (Parameter) WT (kg) 7.2 7.1 7.2 7.1 7.0 7.2 7.3 7.2 7.1 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 533 533 533 533 533 533 533 533 533 WT/WL 0.0135 0.0133 0.0135 0.0133 0.0131 0.0135 0.0137 0.0135 0.0133 T (mm) 8.0 7.9 8.0 8.0 8.0 8.0 8.0 8.0 7.8 E* × T 28.0 27.7 28.0 28.0 28.0 28.0 28.0 37.6 42.9 (Evaluation result) Steering stability 105 108 113 117 120 122 127 130 133 Durability 107 110 115 112 110 115 118 122 126 Comprehensive 212 218 228 229 230 237 245 252 259 evaluation

TABLE 4 Comparative Example 2-1 2-2 2-3 2-4 2-5 2-6 2-7 2-8 2-9 2-10 (Mixing) NR 5 5 5 5 5 5 5 5 5 5 SBR 75 75 75 75 75 75 75 75 90 90 BR 20 20 20 20 20 20 20 20 5 5 Carbon black 4 4 4 4 4 4 4 4 4 4 Silica 55 55 55 55 55 55 55 55 55 55 Silane coupling agent 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 Oil 45 45 45 45 45 45 45 45 20 10 Resin 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 1 wax 1 1 1 1 1 1 1 1 1 1 stearic acid 1 1 1 1 1 1 1 1 1 1 sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 2 1 × 2 1 × 2 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.59 0.59 0.59 0.59 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 42 42 55 42 42 55 55 55 55 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.7 0.7 0.7 0.45 0.45 0.45 0.45 Angle (°) 100 100 100 100 100 100 100 60 60 60 (Parameter) WT (kg) 7.6 7.3 7.5 7.6 7.4. 7.5 7.5 7.9 7.6 7.6 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 533 533 533 533 533 533 533 533 533 533 WT/WL 0.0143 0.0137 0.0141 0.0143 0.0139 0.0141 0.0141 0.0148 0.0143 0.0143 T (mm) 8.5 8.0 8.5 8.5 8.3 8.5 8.4 9.1 8.5 8.5 E* × T 29.8 28.0 29.8 29.8 29.1 29.8 29.4 31.9 40.0 46.8 (Evaluation result) Steering stability 88 85 90 88 85 90 95 92 95 100 Durability 88 82 92 85 80 90 88 90 98 100 Comprehensive 176 167 182 173 165 180 183 182 193 200 evaluation

[Experiment 3]

In this experiment, a tire having a tire size of 215/55R17 (outer diameter Dt: 668 mm, cross-sectional width Wt: 226 mm, virtual volume V: 46109661 mm³) was prepared and evaluated.

After manufacturing each of the test tires shown in Tables 5 and 6 in the same manner as in Experiment 1, each parameter was obtained in the same manner. Then, in the same manner, a performance evaluation test was conducted and evaluated. The steering stability was evaluated with the result in Comparative Example 3-10 as 100, and the durability performance was also evaluated with the result in Comparative Example 3-10 as 100. The results of each evaluation are shown in Tables 5 and 6.

TABLE 5 Example 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 (Mixing) NR 5 5 5 5 5 5 5 5 5 SBR 90 90 90 90 90 90 90 90 90 BR 5 5 5 5 5 5 5 5 5 Carbon black 4 4 4 4 4 4 4 4 4 Silica 50 50 50 50 50 50 50 55 55 Silane coupling agent 5 5 5 5 5 5 5 5.5 5.5 Oil 20 20 20 20 20 20 20 20 10 Resin 25 25 25 25 25 25 25 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 Wax 1 1 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 55 55 55 55 55 75 90 75 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.45 0.22 0.45 0.45 0.45 0.45 Angle (°) 100 60 46 46 46 46 46 46 46 (Parameter) WT (kg) 8.3 8.2 8.3 8.2 8.1 8.3 8.4 8.3 8.2 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 607 607 607 607 607 607 607 607 607 WT/WL 0.0137 0.0135 0.0137 0.0135 0.0133 0.0137 0.0138 0.0137 0.0135 T (mm) 8.5 8.4 8.5 8.5 8.5 8.5 8.5 8.5 8.3 E* × T 29.8 29.4 29.8 29.8 29.8 29.8 29.8 40.0 45.7 (Evaluation result) Steering stability 108 112 115 120 125 128 130 133 138 Durability 104 107 110 111 108 112 113 116 120 Comprehensive 212 219 225 231 233 240 243 249 258 evaluation

TABLE 6 Comparative example 3-1 3-2 3-3 3-4 3-5 3-6 3-7 3-8 3-9 3-10 (Mixing) NR 5 5 5 5 5 5 5 5 5 5 SBR 75 75 75 75 75 75 75 75 90 90 BR 20 20 20 20 20 20 20 20 5 5 Carbon black 4 4 4 4 4 4 4 4 4 4 Silica 55 55 55 55 55 55 55 55 55 55 Silane coupling agent 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 Oil 45 45 45 45 45 45 45 45 20 10 Resin 25 35 Zinc oxide 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Anti-aging agent-1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Anti-aging agent-2 1 1 1 1 1 1 1 1 1 1 Wax 1 1 1 1 1 1 1 1 1 1 Stearic acid 1 1 1 1 1 1 1 1 1 1 Sulfur 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Vulcanization 2 2 2 2 2 2 2 2 2 2 accelerator-1 Vulcanization 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 accelerator-2 (Code) Composition 1 × 2 1 × 2 1 × 2 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 1 × 1 Cord outer diameter 0.59 0.59 0.59 0.59 0.3 0.3 0.3 0.3 0.3 0.3 (mm) Ends e 42 42 55 42 42 55 55 55 55 75 (Belt layer) Average distance (mm) 0.7 0.7 0.7 0.7 0.7 0.7 0.45 0.45 0.45 0.45 Angle (°) 100 100 100 100 100 100 100 60 60 60 (Parameter) WT (kg) 8.7 8.4 8.6 8.7 8.5 8.6 8.6 9 8.7 8.7 E* (MPa) 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 4.7 5.5 WL (kg) 607 607 607 607 607 607 607 607 607 607 WT/WL 0.0143 0.0138 0.0142 0.0143 0.0140 0.0142 0.0142 0.0148 0.0143 0.0143 T (mm) 9.0 8.5 9.0 9.0 8.8 9.0 8.9 9.6 9.0 9.0 E* × T 31.5 29.8 31.5 31.5 30.8 31.5 31.2 33.6 42.3 49.5 (Evaluation results) Steering stability 90 88 91 89 88 90 96 93 94 100 Durability 85 83 88 84 79 88 84 88 95 100 Comprehensive 175 171 179 173 167 178 180 181 189 200 evaluation

From the results of Experiments 1 to 3 (Tables 1 to 6), in any size tire, it can be seen that when the reinforcing cords in the belt layer were configured by arranging 50 monofilaments/5 cm or more, and (formula 1) described above is satisfied, a pneumatic tire having excellent steering stability and durability during high-speed driving can be obtained.

Further, it can be seen that a pneumatic tire having further improved steering stability and durability at high-speed driving can be obtained by the control according to (formula 2) described above, the appropriate control of the outer diameter of the cord, and the like.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the above embodiments within the same and equivalent scope as the present invention. 

1. A pneumatic tire having a tread portion and a belt layer, wherein the tread portion is arranged on the outer side of the belt layer in the tire radial direction, the reinforcing cord in the belt layer is composed of cords made of monofilaments in which 50/5 cm or more of the monofilaments are arranged in the tire width direction in the tire radial cross section of the belt layer, and the maximum load capacity of the tire WL (kg) and the weight of the tire WT (kg) satisfy the following formula
 1. (WT/WL)≤0.0140  formula 1
 2. The pneumatic tire according to claim 1, wherein the outer diameter of the cord made of the monofilaments is 0.1 to 0.5 mm.
 3. The pneumatic tire according to claim 1, wherein the complex elastic modulus E* (MPa) when the tread rubber composition forming the contact surface in the outermost layer of the tread portion is measured under the conditions of temperature: 30° C., initial strain: 5%, dynamic strain: ±1%, frequency: 10 Hz, deformation mode: elongation, and the distance T (mm) from the outermost surface of the tread portion to the outermost surface of the belt layer satisfy the following formula
 2. (E*×T)≥30  formula 2
 4. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of circumferential grooves extending continuously in the tire circumferential direction, and the total cross-sectional area of the plurality of circumferential grooves is 10 to 30% of the cross-sectional area of the tread portion.
 5. The pneumatic tire according to claim 1, wherein the tread portion has a plurality of lateral grooves extending in the tire axial direction, and the total volume of the plurality of lateral grooves is 2.0 to 5.0% of the volume of the tread portion.
 6. The pneumatic tire according to claim 1, wherein at least two layers of the belt layer are provided, and the average distance D (mm) between the belt layers in the tread portion is 0.6 mm or less, in at least one set of belt layers adjacent to each other in the radial direction of the tire.
 7. The pneumatic tire according to claim 1, wherein at least two layers of the belt layer are provided, and the angle between the belt layers in the tread portions in the tire circumferential direction is 65° or less, in at least one set of belt layers adjacent to each other in the radial direction of the tire.
 8. The pneumatic tire according to claim 1, wherein the tread has a circumferential groove extending continuously in the tire circumferential direction, and the ratio (L₈₀/L₀) of the groove width L₈₀ at a depth of 80% of the maximum depth of the circumferential groove to the groove width L₀ of the circumferential groove on the contact surface of the tread portion is 0.3 to 0.7.
 9. The pneumatic tire according to claim 1, wherein the tire cross-sectional width Wt (mm) is less than 200 mm. 